Messages in this thread | | | From | Denys Vlasenko <> | Subject | [PATCH 0/3] x86: do not save callee-preserved registers around lockdep_sys_exit_thunk | Date | Sat, 28 Feb 2015 01:29:18 +0100 |
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Recent change to struct pt_regs handling in entry.S, among other things, changed how callee-preserved registers are saved around call to lockdep_sys_exit_thunk:
# define LOCKDEP_SYS_EXIT_IRQ \ TRACE_IRQS_ON; \ sti; \ SAVE_EXTRA_REGS; \ <======= HERE LOCKDEP_SYS_EXIT; \ RESTORE_EXTRA_REGS; \ <======= HERE
The change is in fact a bit fragile: now we assume that LOCKDEP_SYS_EXIT_IRQ macro is used only when there is a struct pt_regs on the stack.
So far this assumption is true, but it is probably a coincidence.
We can revert back to pushing registers, but this callee-preserved registers saving appears bogus. It is not necessary: they _are_ callee-preserved, and lockdep_sys_exit() does not touch them on the stack either.
First two patches clean up #define maze so that we can see that LOCKDEP_SYS_EXIT macro call above is merely "call lockdep_sys_exit_thunk".
Last patch removes SAVE/RESTORE.
I tested this patch series and everything seems to run fine on a lockdep-enabled kernel with these lines removed.
Denys Vlasenko (3): x86: move ARCH_LOCKDEP_SYS_EXIT[IRQ] defines closer to their users x86: fold ARCH_LOCKDEP_SYS_EXIT defines into their users x86: do not save callee-preserved registers around lockdep_sys_exit_thunk
arch/x86/include/asm/irqflags.h | 45 +++++++++++++++++------------------------ 1 file changed, 19 insertions(+), 26 deletions(-)
CC: Linus Torvalds <torvalds@linux-foundation.org> CC: Steven Rostedt <rostedt@goodmis.org> CC: Ingo Molnar <mingo@kernel.org> CC: Borislav Petkov <bp@alien8.de> CC: "H. Peter Anvin" <hpa@zytor.com> CC: Andy Lutomirski <luto@amacapital.net> CC: Oleg Nesterov <oleg@redhat.com> CC: Frederic Weisbecker <fweisbec@gmail.com> CC: Alexei Starovoitov <ast@plumgrid.com> CC: Will Drewry <wad@chromium.org> CC: Kees Cook <keescook@chromium.org> CC: x86@kernel.org CC: linux-kernel@vger.kernel.org
-- 1.8.1.4
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